[PATCH v5 02/26] rust: alloc: separate `aligned_size` from `krealloc_aligned`

Danilo Krummrich
2024-08-12T18:24:19Z

Separate `aligned_size` from `krealloc_aligned`.

Subsequent patches implement `Allocator` derivates, such as `Kmalloc`,
that require `aligned_size` and replace the original `krealloc_aligned`.

Reviewed-by: Alice Ryhl <aliceryhl@google.com>
Reviewed-by: Benno Lossin <benno.lossin@proton.me>
Signed-off-by: Danilo Krummrich <dakr@kernel.org>
---
rust/kernel/alloc/allocator.rs | 19 ++++++++++++-------
1 file changed, 12 insertions(+), 7 deletions(-)

diff --git a/rust/kernel/alloc/allocator.rs b/rust/kernel/alloc/allocator.rs
index e6ea601f38c6..c83b6dff896d 100644
--- a/rust/kernel/alloc/allocator.rs
+++ b/rust/kernel/alloc/allocator.rs
@@ -8,6 +8,17 @@

struct KernelAllocator;

+/// Returns a proper size to alloc a new object aligned to `new_layout`'s alignment.
+fn aligned_size(new_layout: Layout) -> usize {
+ // Customized layouts from `Layout::from_size_align()` can have size < align, so pad first.
+ let layout = new_layout.pad_to_align();
+
+ // Note that `layout.size()` (after padding) is guaranteed to be a multiple of `layout.align()`
+ // which together with the slab guarantees means the `krealloc` will return a properly aligned
+ // object (see comments in `kmalloc()` for more information).
+ layout.size()
+}
+
/// Calls `krealloc` with a proper size to alloc a new object aligned to `new_layout`'s alignment.
///
/// # Safety
@@ -15,13 +26,7 @@
/// - `ptr` can be either null or a pointer which has been allocated by this allocator.
/// - `new_layout` must have a non-zero size.
pub(crate) unsafe fn krealloc_aligned(ptr: *mut u8, new_layout: Layout, flags: Flags) -> *mut u8 {
- // Customized layouts from `Layout::from_size_align()` can have size < align, so pad first.
- let layout = new_layout.pad_to_align();
-
- // Note that `layout.size()` (after padding) is guaranteed to be a multiple of `layout.align()`
- // which together with the slab guarantees means the `krealloc` will return a properly aligned
- // object (see comments in `kmalloc()` for more information).
- let size = layout.size();
+ let size = aligned_size(new_layout);

// SAFETY:
// - `ptr` is either null or a pointer returned from a previous `k{re}alloc()` by the
--
2.45.2